Such pressure sensors include, as a rule, a measuring mechanism having a high-pressure chamber on one side and a low pressure chamber on the other. These chambers are each sealed by a dividing membrane, also called a separating diaphragm, and are filled with a transfer medium. The dividing membranes are loaded, respectively, with a pressure acting on the high-pressure side and a pressure acting on the low-pressure side. The two pressures are transferred by way of the dividing membranes into the respective chambers. The chambers are separated from one another by a sensor element. The sensor element includes a pressure-sensitive element, especially a measuring membrane, which is loaded on its first surface with the hydraulic pressure in the chamber of the high-pressure side and on its second surface with the hydraulic pressure in the chamber of the low-pressure side. Particularly pressure-sensitive elements made of semiconductor materials exhibit such a stiffness, that the volume displacement at the pressure-sensitive element is practically negligible over the entire measuring range. This makes these pressure-sensitive elements, however, very sensitive to overloads, since there is hardly any elasticity present to absorb them. Destruction of the measuring cell can result. A static overload protection is usually provided by having a mechanical overload protector push liquid, in the case of a unilateral overload, from the high-pressure side to the low-pressure side (or vice versa) and by having the dividing membranes come to rest on respective surfaces. This prevents a further increase in pressure.
Dynamic overload peaks in the form of pressure shocks present another problem. It is true that designs of differential pressure sensors are oriented toward structuring the cells on both sides, the high-pressure (HP) side and the low-pressure (LP) side, to a large extent symmetrically (same routing, liquid volumes, membranes, etc.), in order to minimize temperature and pressure errors, but asymmetries, at least with regard to dynamic behavior, cannot always be avoided, because of other boundary conditions. In the case of dynamic, bilateral loads, such as pressure shocks during hot steam measurements, pulses from piston pumps, concussions in closed container systems, these lead to travel time differences between the HP and the LP sides and, consequently, to associated, transient pressure peaks at the sensor. The chip is destroyed and the device stops working.
Simple lessening of the diameter, for example, of the pressure supply line between the chamber on the high-pressure side and the pressure-sensitive element does not effectively damp the pressure spikes.
German Offenlegungsschrift (laid open Patent Application) DE 376 13 236 A1 discloses a pressure sensor, in which a sintered metal plate or a steel plate with a bore or a plurality of parallel bores of, at most, 0.5 mm diameter are inserted between the process and the measuring cell. This solution is unsatisfactory for a number of reasons. On the one hand, the reduction of the hydraulic path between process and measuring cell to even a single bore of 0.5 mm diameter with a bore length in keeping with the illustrated plate thickness does not, by far, provide sufficient damping to suppress spike-type overload pressure shocks. If, on the other hand, a damping element is provided that has sufficiently large flow resistance for an effective damping, then the reaction velocity of the differential pressure sensor is significantly slowed, so that pressure fluctuations that are within the measurement range of the sensor are then only registered after a delay.
An object of the present invention is, therefore, to provide a differential pressure sensor which overcomes the above-described disadvantages.